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Max span of oak/wood beam without sagging

Postby pipedream72 » Mon Jul 11, 2022 2:33 pm

Hi, I am looking to create a sort of tunnel pergola made up of a series of square shaped arches (literally just two vertical posts and a horizontal span). Somehting along the lines of this but without the archs all connected together - ... -archways/

The arches are likely to be about 6 metres wide, but that feels like it might be wide enough that the horizontal span will start sagging. I was thinking of building it with something like 150mm or 200mm oak beams, but there might be other types of wood that are better for this and less prone to sagging?

Is there a way that I can work out what thickness of beams I would need to avoid any sagging over a given span? And are there any woods that would particularly lend themselves to build this type of structure?

Thanks for any advice,

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Simply Build It

Postby stoneyboy » Thu Jul 14, 2022 8:47 pm

Hi pipedream72,
You will definitely end up with sagging over a 6m span no matter which timber you use.
Oak will be a nightmare because it will split and twist all over the place.
I suggest you make enquiries of a timber stockist because 6m lengths are unlikely to be available except to special order.
Regards S
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